In this study, a near-infrared (NIR)-responsive hydrogel based on ethylenediamine (EDA)-functionalized Gellan Gum was developed through a simple preparation method. This hydrogel incorporates in situ synthesized polydopamine (pDA) and was loaded with first- and second-generation antimicrobial bis-MPA polyester dendrimers (TMP-G1-[Cys]6 and MP-G2-[Cys]12), bearing cysteamine hydrochloride as peripheral functional groups. The intrinsic ability of pDA to scavenge reactive oxygen species (ROS) and convert NIR light at 810 nm into heat imparted radical scavenging activity and photothermal properties to the systems. It has been demonstrated that, due to the noncovalent interactions with both GG-EDA and pDA, dendrimers are retained differently within the sample depending on their molecular weight and the number of terminal positive charges. This difference in retention influences their antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In particular, it has been shown that the NIR-induced photothermal effect plays a crucial role in triggering the activity of the sample loaded with the most retained dendrimer, which possesses the highest number of terminal positive charges. The high physiological fluid absorption capacity makes these materials ideal for wound exudate management. In addition, their resistance to hydrolytic degradation can be exploited to reduce the frequency of dressing changes, potentially improving patient comfort. The dendrimer-loaded samples demonstrated low cytotoxicity toward human fetal dermal mesenchymal stromal cells (FD-MSCs) and human epidermal keratinocytes (HaCaT). These findings suggest that GG-EDA@pDA+TMP-G1-[Cys]6 or TMP-G2-[Cys]12 could be promising candidates for the treatment of infected skin wounds.

The standard-of-care for treating complex bone fractures includes metal screws and plates. However, their rigid, pre-shaped geometry, coupled with a lack of patient-specific customization and degradability, often results in post-surgical complications and the need for secondary surgeries. Alternatives that are adaptable, biodegradable, and versatile enough to address these limitations have become a priority for the surgical community. Injectable viscous mixtures that harden on demand into composites present a compelling solution, as they can mimic the mechanical properties of bone and conform to any fracture geometry. One promising example evaluated in preclinical trials is clickable composites based on triazine-2,4,6-trione (TATO)-based allyl and thiol monomers combined with hydroxyapatite fillers. These materials cure via visible light-induced thiol-ene coupling chemistry, providing adequate stiffness and strength for bone healing. However, the lack of degradability in these composites has limited their broader application. To overcome this limitation, we developed a new generation of TATO composites with hydrolytically degradable ester linkages and bioresorbable fillers. Offering exceptional versatility, these advanced materials can be cast into twistable films or injected to form high-strength composites. Hydrolysis testing revealed a 41%-64% increase in mass loss compared to the non-degradable TATO composites, while maintaining a high flexural modulus up to 6.4 GPa and a softening temperature above 45 degrees C, well above body temperature. When evaluated as fracture fixation patches, the degradable composites demonstrated superior performance, including greater load capacity and flexibility, compared to their non-degradable counterparts. By delivering strong mechanical support throughout the bone healing process and seamlessly degrading over time, these composites can indeed pave the way for a new era in orthopedic care, where versatile, biodegradable materials not only address critical clinical challenges but also set a visionary standard for the future of patient-centered surgical solutions.

Selenium (Se) is a highly biologically active element, and its organic derivatives have attracted growing interest for their promising chemotherapeutic potential, largely due to their redox-modulating activity, which selectively affects cancer cells with high levels of reactive oxygen species (ROS). However, their high reactivity and susceptibility to spontaneous degradation limit their biomedical application. To harness their potential in the realm of nanomedicine, we present a new generation of therapeutically promising polymers that combine Se with 2,2-bis(methylol)propionic acid (bis-MPA)-based dendritic polymers, chosen for their high chemical versatility, low toxicity, and excellent biodegradability. Most examples in the literature about dendritic polymers feature dormant dendritic skeletons with active functional groups expressed only on their periphery, which severely limits their functional scope. In this work, monodisperse dendrimers and linear-dendritic (LD) polymers up to the third generation were developed, with the latter capable of self-assembling into dendritic micelles (similar to 20 nm). These systems feature Se at the dendritic core or peripheral branches in the form of monoselenide or diselenide bridges. Selenium incorporation demonstrated excellent compatibility with two key polyester synthetic approaches: anhydride chemistry and fluoride-promoted esterification (FPE). Both monoselenide and diselenide linkages introduced degradability and dynamic behavior in dendrimers and dendritic micelles. However, their biological activities differed significantly. Diselenide-containing dendrimers exhibited great anticancer potential against breast cancer cell lines, with IC50 values in the micromolar range. Among these, first-generation Se dendrimers stood out due to their promising selectivity toward cancer cells. In contrast, dendritic polymers incorporating monoselenides retained the high biocompatibility characteristics of bis-MPA dendritic constructs.

Antibiotic-resistant pathogens have been declared by the WHO as one of the major public health threats facing humanity. For that reason, there is an urgent need for materials with inherent antibacterial activity able to replace the use of antibiotics, and in this context, hydrogels have emerged as a promising strategy. Herein, we introduce the next generation of cationic hydrogels with antibacterial activity and high versatility that can be cured on demand in less than 20 s using thiol-ene click chemistry (TEC) in aqueous conditions. The approach capitalizes on a two-component system: (i) telechelic polyester-based dendritic-linear-dendritic (DLDs) block copolymers of different generations heterofunctionalized with allyl and ammonium groups, as well as (ii) polyethylene glycol (PEG) cross-linkers functionalized with thiol groups. These hydrogels resulted in highly tunable materials where the antibacterial performance can be adjusted by modifying the cross-linking density. Off-stoichiometric hydrogels showed narrow antibacterial activity directed toward Gram-negative bacteria. The presence of pending allyls opens up many possibilities for functionalization with biologically interesting molecules. As a proof-of-concept, hydrophilic cysteamine hydrochloride as well as N-hexyl-4-mercaptobutanamide, as an example of a thiol with a hydrophobic alkyl chain, generated three-component networks. In the case of cysteamine derivatives, a broader antibacterial activity was noted than the two-component networks, inhibiting the growth of Gram-positive bacteria. Additionally, these systems presented high versatility, with storage modulus values ranging from 270 to 7024 Pa and different stability profiles ranging from 1 to 56 days in swelling experiments. Good biocompatibility toward skin cells as well as strong adhesion to multiple surfaces place these hydrogels as interesting alternatives to conventional antibiotics.

Open reduction internal fixation metal plates and screws remain the established standard-of-care for complex fracture fixation. They, however, have drawbacks such as limited customization, soft-tissue adhesions, and a lack of degradation. Bone cements and composites are being developed as alternative fixation techniques in order to overcome these issues. One such composite is a strong, stiff, and shapeable hydroxyapatite-containing material consisting of 1,3,5-triazine-2,4,6-trione (TATO) monomers, which cures through high energy visible light-induced thiol–ene coupling (TEC) chemistry. Previous human cadaver and in vivo studies have shown that patches of this composite provide sufficient fixation for healing bone fractures; however, the composite lacks degradability. To promote degradation through hydrolysis, new allyl-functionalized isosorbide-based polycarbonates have been added into the composite formulation, and their impact has been evaluated. Three polycarbonates with allyl functionalities, located at the termini (aPC1 and aPC2) or in the backbone (aPC3), were synthesized. Composites containing 1, 3, and 5 wt % of aPCs 1–3 were formulated and evaluated with regard to mechanical properties, water absorption, hydrolytic degradation, and cytotoxicity. Allyl-functionalized polycaprolactone (aPCL) was synthesized and used as a comparison. When integrated into the composite, aPC3 significantly impacted the material’s properties, with the 5 wt % aPC3 formulation showing a significant increase in degradation of 469%, relative to the formulation not containing any aPCs after 8 weeks’ immersion in PBS, along with a modest decrease in modulus of 28% to 4.01 (0.3) GPa. Osteosyntheses combining the aPC3 3 and 5 wt % formulations with screws on synthetic bones with ostectomies matched or outperformed the ones made with the previously studied neat composite with regard to bending stiffness and strength in four-point monotonic bending before and after immersion in PBS. The favorable mechanical properties, increased degradation, and nontoxic characteristics of the materials present aPC3 as a promising additive for the TATO composite formulations. This combination resulted in stiff composites with long-term degradation that are suitable for bone fracture repair.

Heterofunctional polyester dendrimers up to the third generation, containing 21 internally queued bromine atoms, have been successfully synthesized for the first time using a divergent growth approach. Direct azidation reactions enabled the conversion of the bromide groups to clickable azide pendant functionalities. Therapeutic and chemical moeities could then be coupled to the internal azide or bromide functionalities and external hydroxyl groups of the heterofunctional dendrimers through CuAAC, thiol-bromo click and esterification reactions, expanding their potential for biomedical applications.

Structurally perfect cationic polyester dendrimers based on 2,2 dimethylolpropionic acid (bis-MPA) were exploited in combination with anionic cellulose nanofibrils (CNFs) in the fabrication of a comprehensive library of electrostatically cross-linked hybrid hydrogels. Three distinct families of cationic bis-MPA dendrimers ranging from first to third generation were used, displaying up to 24 peripheral ammonium groups. The dendrimer families covering different hydrolytic stability and peripheral ammonium groups, β-alanine, cysteamine hydrochloride, and N,N-dimethylcysteamine hydrochloride were chosen as ammonium groups. The self-assembly process occurred spontaneously without external stimuli, resulting in well-organized and self-supporting hydrogels. The water content of the hydrogels reached values up to 99.6 wt % with a storage modulus ranging from 1.2 to 3.0 kPa which is within the range of skin tissue. The antibacterial activity of the dendrimers and the formed hydrogels was evaluated against Gram-negative and Gram-positive bacteria strains, and the cytotoxicity was determined by measured cell viability prevention of diverse cell lines. The hydrogels based on TMP-G1-[Cys]6 exhibited the highest antibacterial activity without showcasing toxicity. To demonstrate its effectiveness, the hydrogel was freeze-dried, resulting in a porous aerogel that exhibited significantly greater antibacterial activity than commercially available band-aids.

Hydroxyapatite (HA) infused triazine-trione (TATO) composites have emerged as an injectable platform for customizable bone fixators due to their fast and benign curing via high-energy visible light-induced thiol-ene chemistry (HEV-TEC), promising mechanical performance, and preclinical outcomes. These composites can overcome many of the existing limitations accompanying metal implants such as poor patient customizability, soft tissue adhesions, and stress shielding. Taking into account that the promising benchmarked TATO composite (BC) is based on stable sulfur-carbon bonds, we herein investigate the impact of introducing polyester dendritic cross-linkers based on bis-MPA as chemically integrated branched additives that display labile esters in a branched configuration. The inclusion of dendrimers, G1 and G3, in concentrations of 1, 3, and 5 wt % in the composite formulations were found to (i) decrease the processing viscosity of the composite formulations, reaching Newtonic and nonshear thinning behavior at 37 degree celsius and (ii) impact the size distribution of bubble cavities in the composite cross sections. The lowest collected T-g for the dendrimer-containing composites was noted to be 73.2 degree celsius, a temperature well above physiological temperature. Additionally, all composites displayed flexural modulus above 6 GPa and flexural strength of ca. 50 MPa under dry conditions. The composites comprising 5 wt % of G1 and G3 dendrimers, with ester bond densities of 0.208 and 0.297 mmol/g, respectively, reached a mass loss up to 0.27% in phosphate buffered saline at 37 degree celsius, which is within the range of established polycaprolactone (PCL). Combined with the nontoxic properties extracted from the cell viability study, polyester dendrimers were determined as promising additives which compatibilized well with the TATO formulation and cross-linked efficiently resulting in strong composites suited for bone fracture fixations.

Polyester dendrimers based on 2,2 bis(hydroxymethyl)propionic acid have been reported to be degradable, non-toxic, and exhibit good antimicrobial activity when decorated with cationic charges. However, these systems exhibit rapid depolymerization, from the outer layer inwards in physiological neutral pHs, which potentially restricts their use in biomedical applications. In this study, we present a new generation of amine functional bis-MPA polyester dendrimers with increased hydrolytic stability as well as antibacterial activity for Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) planktonic bacteria strains. These new derivatives show generally good cytocompatibility for the concentrations they are active toward bacteria, in monocyte/macrophage-like cells (Raw 264.7), and human dermal fibroblasts. Fluoride - promoted esterification chemistry, anhydride chemistry, and click reactions were utilized to produce a library from generations 1–3 and with cationic peripheral groups ranging from 6 to 24 groups, respectively. The dendrimers were successfully purified using conventional purification techniques as well as characterized by matrix-assisted laser desorption ionization time-of-flight mass spectroscopy, nuclear magnetic resonance, and size exclusion chromatography. As proof of synthetic versatility, dendritic-linear-dendritic block copolymer were successfully synthesized to display cysteamine peripheral functionalities as well as the scaffolding ability with biomedically relevant lipoic acid and methoxy polyethylene glycol.

Polymer thermosets and composites based on rigid trizaine-trione (TATO) alkene and thiol monomers show great promise as bone fixation materials and dental composites due to their ability to efficiently crosslink via thiol-ene coupling chemistry into stiff and strong materials. In order to broaden the scope of these materials, a TATO thermoset was optimized for sterolithography (SLA) 3D printing through the addition of either a diluent (PETMP) and photo-absorber (Sudan I), or the addition of a free radical inhibitor (pyrogallol). A 3D printable hydroxyapatite (HA) composite was also formulated by adding a combination of nano-HA and micro-HA particles, which were found to increase the thermal stability and modulus of the material, respectively. The modulus of the printed thermosets containing Sudan I and pyrogallol exceeded any previously published acrylate-free thiol-ene SLA resins, at 1.6 (0.1) and 1.85 (0.06) GPa, respectively. The printed HA composite formulation had a modulus of 2.4 (0.2) GPa. All three formulations showed a comparable resolution to a commercially available SLA resin and were non-toxic toward Raw 264.7 and human dermal fibroblast cells. These results demonstrate the potential of TATO based SLA resins for the construction of strong, fully-customizable, printed implants for biomedical applications.